Slight refactor git cl diff.

git_cl.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Copyright (C) 2008 Evan Martin <martine@danga.com>
 
 """A git-command for integrating reviews on Rietveld and Gerrit."""
 
 from distutils.version import LooseVersion
@@ skipping 974 matching lines @@
         return None
       self.branchref = branchref
       self.branch = ShortBranchName(self.branchref)
     return self.branch
 
   def GetBranchRef(self):
     """Returns the full branch name, e.g. 'refs/heads/master'."""
     self.GetBranch()  # Poke the lazy loader.
     return self.branchref
 
+  def ClearBranch(self):
+    """Clears cached branch data of this object."""
+    self.branch = self.branchref = None
+
   @staticmethod
   def FetchUpstreamTuple(branch):
     """Returns a tuple containing remote and remote ref,
        e.g. 'origin', 'refs/heads/master'
     """
     remote = '.'
     upstream_branch = RunGit(['config', 'branch.%s.merge' % branch],
                              error_ok=True).strip()
     if upstream_branch:
       remote = RunGit(['config', 'branch.%s.remote' % branch]).strip()
@@ skipping 3305 matching lines @@
   cl = Changelist(auth_config=auth_config)
   issue = cl.GetIssue()
   branch = cl.GetBranch()
   if not issue:
     DieWithError('No issue found for current branch (%s)' % branch)
   TMP_BRANCH = 'git-cl-diff'
   base_branch = cl.GetCommonAncestorWithUpstream()
 
   # Create a new branch based on the merge-base
   RunGit(['checkout', '-q', '-b', TMP_BRANCH, base_branch])
-  # Update the cached branch in cl instance, to avoid overwriting original
-  # branch properties.
-  cl.branch = cl.branchref = None
+  # Clear cached branch in cl object, to avoid overwriting original CL branch
+  # properties.
+  cl.ClearBranch()
   try:
     rtn = cl.CMDPatchIssue(issue, reject=False, nocommit=False, directory=None)
     if rtn != 0:
       RunGit(['reset', '--hard'])
       return rtn
 
     # Switch back to starting branch and diff against the temporary
     # branch containing the latest rietveld patch.
     subprocess2.check_call(['git', 'diff', TMP_BRANCH, branch, '--'])
   finally:
@@ skipping 291 matching lines @@
 if __name__ == '__main__':
   # These affect sys.stdout so do it outside of main() to simplify mocks in
   # unit testing.
   fix_encoding.fix_encoding()
   setup_color.init()
   try:
     sys.exit(main(sys.argv[1:]))
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)